JPH0885005A - Variable air bearing device - Google Patents

Abstract

PURPOSE: To provide a bearing device in which a radial gap at every part of a revolving shaft can be made almost uniform ranging over a wide range from a low speed area to a high speed area, the bearing performance is stable, no unstable vibration occurs, and the reliability against the distrubance is not lowered. CONSTITUTION: In a high speed air bearing device consisting of a stationary member 1, a rotary member 2, which is able to rotate with respect to the stationary member 1, and a radial air bearing body 4, which is placed between the stationary member 1 and the rotary member 2, this variable air bearing device contains a controlling means with which the radial air bearing body 4 can be moved in the radial direction via a driving means 8, 11 while the gap between the stationary member 1 and the rotary member 2 can be changed in accordance with the number of revolutions of the rotary member 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed rotary air bearing device comprising a stationary member, a rotating member rotatable with respect to the stationary member, and a radial air bearing body provided between the stationary member and the rotating member.

[0002]

2. Description of the Related Art Spindles that employ roller bearings are equipped with oil and
Various lubrication methods such as air lubrication and under-race lubrication have been developed, but it is said that a DN value of about 3 million is the limit, and it is difficult to achieve higher speeds.

On the other hand, a high-speed rotating shaft using an air bearing is supported by a non-contact bearing, has little power loss and heat generation due to rotation, and is suitable for high-speed rotation with a slight bearing power (friction) loss. There is.

When the air bearing is applied to high speed rotation,
It is known that the clearance decreases due to centrifugal force expansion of the shaft and thermal expansion due to friction, which causes contact and seizure accidents.To avoid this danger, it is common to design with a wide clearance in advance. .

Therefore, inadequate load capacity and insufficient rigidity in the low-speed range cannot be denied, and air bearings have generally been rarely used for cutting spindles.

Accordingly, the rigidity at low speed is secured to some extent,
If an air bearing capable of high-speed rotation can be realized, a spindle suitable for use from low speed to high speed can be provided as a cutting spindle.

In Japanese Patent Laid-Open No. 1-135919, it is detected that the gap between the rotary shaft and the fluid bearing fluctuates due to the heat generated in the bearing, as fluctuation in the flow rate of the pressurized fluid fed into the gap. Disclosed is a method and a device for controlling a clearance of a fluid bearing, which controls an electric power supplied to a Peltier element of a cooling device provided in the fluid bearing based on the flow rate fluctuation.

Further, in Japanese Patent Laid-Open No. 1-210617, a bearing gap of a hydrostatic gas bearing that rotatably supports a hollow rotary shaft is detected, and the above bearing is proportional to the size of the detected bearing gap. Disclosed is a method and apparatus for controlling the rigidity of a static pressure gas bearing, which is characterized in that the pressure of the supplied gas is controlled to maintain the rigidity of the bearing.

[0009]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the method and apparatus disclosed in Japanese Patent No. 35919, a gap is detected as a flow rate fluctuation of a pressurized fluid due to a flow rate fluctuation of a gas supplied to an air bearing, and electric power input to a Peltier element cooling a bearing portion. However, in such a case, the heat generated in the bearing is cooled to suppress the heat generation, thereby making the gap have a desired size. Since it serves as a medium, the control response to the gap change is poor and the control is not performed sufficiently accurately, which does not directly lead to an increase in rigidity at high speed rotation.

In the method disclosed in Japanese Patent Laid-Open No. 1-210617, the gap itself is not controlled, but the pressure is controlled. Therefore, the rigidity decrease compensable by this method is excessive at low speeds. Although the clearance is controlled by pressure, the pressure is lower at high speed than at low speed, and sufficient rigidity cannot be obtained.

[0011]

SUMMARY OF THE INVENTION The present invention solves the problems associated with the prior art described above, and makes it possible to make the radial clearances of the various parts of the rotary shaft uniform over a wide range from the low speed range to the high speed range, thus stabilizing the bearing performance. Therefore, it is an object of the present invention to provide a high-speed rotating shaft in which unstable vibration does not occur and reliability with respect to disturbance does not decrease.

[0012]

SUMMARY OF THE INVENTION In the present invention, a high speed rotation comprising a stationary member, a rotating member rotatable with respect to the stationary member, and a radial air bearing body provided between the stationary member and the rotating member. In the air bearing device, the radial air bearing body is moved in the radial direction via a driving means, and the gap between the radial air bearing body and the rotating member is changed according to the rotation speed of the rotating member. By the variable air bearing device characterized by including a control means,
To achieve the above objectives.

[0013]

In order to provide an air bearing spindle suitable for machining from low speed to high speed, it is necessary to secure rigidity at low speed to some extent and to realize an air bearing capable of high speed rotation. .

For this purpose, an air bearing spindle equipped with a bearing diameter changing device capable of freely changing the clearance narrows the clearance at a low speed to increase rigidity and enables relatively heavy cutting, and at a high speed range. It is necessary to widen the gap and control the gap to prevent contact and seizure.

At this time, the rotating shaft and the bearing follow the following deformation process with the rotation. In other words, it is considered that the shaft begins to expand in the radial direction due to the centrifugal force due to the rotation, and the temperature of the shaft and the bearing rises due to the air film heat generation in the bearing gap due to the rotation, which causes thermal expansion, resulting in a decrease in the gap. .

Therefore, in order to properly control the clearance between the bearing and the shaft, it is necessary to know the centrifugal expansion and the respective thermal expansions, but it is often difficult to directly measure these amounts during rotation.

Therefore, in the present invention, the centrifugal force expansion is utilized in proportion to the rotational speed, and the thermal expansion from the measured rotational speed is made in advance from the measured values of the respective bearing temperature and shaft temperature. The expansion amount is calculated by the above conversion formula, the actual clearance is calculated from the expansion amount, and the variable bearing diameter device is controlled so that the bearing clearance becomes the target value determined separately.

That is, a sensor for measuring the number of revolutions, a sensor for measuring the temperature, a conversion unit incorporating a conversion formula for the thermal expansion amount, a storage unit for storing the target clearance, and a difference between the target and the bearing diameter There is provided an air bearing control device having a command unit for converting into a control amount of a conversion device and a drive device for driving a variable device thereby.

Since a contact-fixed temperature sensor cannot be used to measure the shaft temperature, either a non-contact temperature sensor is used, or the shaft temperature is almost equal to the bearing temperature. There is a representative method.

[0020]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a variable type air bearing device for grinding according to the present invention, which is supported by an air bearing, and a case body 1 which is a stationary member of the present invention has a substantially cylindrical shape. Opening 1b in the center of the left wall of 1
The shaft 2 penetrates through the opening 1b as the rotating member of the present invention. A grindstone is fixed to the left end of the shaft 2.

Conical recesses 1c are formed in the front and rear portions of the case body 1 in the axial direction, and radial air bearing bodies 4 having a truncated conical outer periphery are fitted in the recesses 1c in correspondence with the conical recesses 1c. Has been done. A circular hole 4c is formed in the radial air bearing body 4 corresponding to the shaft 2, and the shaft 2 is inserted into the circular hole 4c with a predetermined gap.

Bearing air is jetted from a compressed air supply passage 1a formed in the case body 1 through a jet port 4a radially formed in the radial air bearing body 4.

With the above structure, a static pressure radial air bearing is formed between the case body 1 and the shaft 2, and the shaft 2 is rotatable in the case body 1. Note that FIG. 2 is a cross-sectional view taken along the line AA showing the ejection ports 4a formed radially.

The radial air bearing body has a structure as shown in FIG. That is, there are a proper number of spring portions in the circumferential direction (in FIG. 2, there are two portions where T-shaped grooves are formed, and two portions where they are connected by a bending member), which allows the radial air bearing body 4 to be formed. Can be contracted in the circumferential direction, so that the outer circumference of the radial air bearing body and the inner diameter of the circular hole can be reduced or expanded accordingly. The shape and number of the spring portion may be changed as appropriate.

The small diameter portion side of the truncated cone-shaped radial air bearing body 4 has a columnar shape, and a male screw 4b is engraved on this columnar portion. A female screw 11a formed on the worm wheel 11 is screwed into the columnar portion on which the male screw 4b is engraved.

The outer peripheral portion of the worm wheel 11 is screwed into the worm 8, and the worm 8 is connected to the output shaft of an electric motor (not shown) directly or via an appropriate connecting member such as a gear. . In this embodiment, a stepping motor is used as the electric motor. Therefore, when the electric motor is rotated, the worm 8 is rotated to the left or right according to the rotation direction thereof, and accordingly, the worm wheel 11 is rotated about the shaft 2 in a plane orthogonal to the drawing of FIG. Warm Wheel 1 accordingly
The internal thread 11a provided in 1 and the external thread 4b formed in the cylindrical portion of the radial air bearing body 4 are screwed together to move the radial air bearing body 4 to the left and right.

The tapered outer peripheral surface of the radial air bearing body 4 is engaged with the recess 1c of the case body 1, and is moved by moving the radial air bearing body 4 left and right (longitudinal direction of the shaft 2). Depending on the direction, the radial air bearing body 4 is radially contracted or expanded.

A flange-shaped projection 2a is formed on the left side of the radial air bearing body 4 on the left side of the shaft 2, and a pair of thrust bearing bodies 14a and 14b are provided on the case body 1 so as to face both side surfaces of the flange-shaped projection 2a. The thrust bearing air is provided from the case body 1 through the thrust bearing bodies 14a and 14b, and the collar-shaped projection 2 is provided.
It is injected into a and receives the thrust load of the shaft 2.

On the circumferential surface of the flange-shaped projection 2a, for example, a black tape 2c is attached while leaving a part thereof so that only a part thereof is reflected. Further, a reflection type rotation sensor 10 is provided so as to face the outer peripheral surface of the flange-shaped protrusion 2a, and the rotation number of the shaft 2 and the bearing is measured by detecting the passage of the reflection portion due to the rotation of the shaft by the reflection type rotation sensor 10. It is supposed to do.

In the above embodiment, the collar-shaped protrusion 2a is used.
Although the black tape 2c was pasted leaving a part of the outer peripheral surface of the reflective portion, a gear or the like may be attached to an appropriate portion of the shaft 2 and the number of revolutions may be detected by detecting the teeth of the gear. Alternatively, the frequency of the input current supplied to the stator member 7, which will be described later, may be measured to detect the rotation speed of the rotary shaft 2.

In the embodiment shown in FIG. 1, the contact type thermocouple sensor 12 is attached to the radial air bearing body 4 with an adhesive agent, solder or the like to measure the bearing temperature. The sensor for detecting the bearing temperature is not limited to the above-mentioned contact type thermocouple sensor, and a conventionally known sensor can be used.

Further, a non-contact type radiation temperature sensor 13 is attached in the vicinity of the peripheral surface of the shaft 2 so that the temperature of the shaft 2 itself can be detected.

As shown in FIG. 1, the central portion of the shaft 2 is carved as indicated by reference numeral 2b, and a magnet serving as a rotor member 5 is attached to the carved portion 2b.

As shown in FIG. 1, a coil serving as the stator member 7 of the motor is attached to the center of the case body 1 which is a stationary member, and the rotor member 5 and the stator member 7 correspond to each other. It is located so that An exciting current is supplied to the stator member 7 from a cord.

A control configuration diagram in the embodiment shown in FIG. 1 described above will be described with reference to FIG. 3. The rotation sensor 10 provided facing the flange-shaped projection 2a is electrically connected to the CPU via an amplifier and an A / D converter. Connected to each other. Further, the temperature sensors 12 provided on the two radial air bearing bodies 4 are also connected to the CPU via an amplifier and an A / D converter, respectively. The temperature sensor 13 for detecting the shaft temperature is an amplifier, A
It is connected to the CPU via the / D converter. C based on signals from these temperature sensors 12, 13 and rotation sensor 10
The PU controls the electric current of the stator member 7 through the control device so that the rotational speed of the shaft 2 can be controlled. Further, the driving means of the pulse motor connected to the worm 8 is controlled through the control device.

Next, the control method will be described with reference to FIG. For centrifugal expansion, use the fact that it is proportional to the number of revolutions,
The rotation speed of the shaft 2 is detected, and the expansion amount due to the centrifugal force is calculated based on the rotation speed N. Expansion amount U with K ₀ as a proportional constant
= K ₀ · N ² .

The initial clearance of the bearing is measured when the apparatus of the present invention is stopped or assembled, and is input as Y. Also,
The temperature T of the radial air bearing body is measured by the bearing temperature sensor 12.
Measure ₁ while inputting the initial temperature T ₀₁ . The temperature difference ΔT ₁ = T ₁ −T ₀₁ is calculated from the measured values, and the thermal expansion amount V = K ₁ · ΔT ₁ of the bearing is calculated based on the temperature difference (K ₁ is a proportional constant).

Similarly, the temperature T _{2 of the} shaft 2 is measured by the bearing temperature sensor 1
3 and measure the temperature difference ΔT ₂ from the initial temperature T ₀₂ by ΔT ₂ =
Calculated as T ₂ −T ₀₂ , the amount of thermal expansion of the shaft W = K ₂ · ΔT ₂
(K ₂ is a proportional constant).

Based on these values, the clearance X between the current shaft 2 and the bearing 4 is calculated as X = (Y + V)-(U + W).

On the other hand, the target clearance Z with respect to the desired rotational speed is preliminarily input to the CPU for each rotational speed in consideration of the rigidity of the air bearing, the ease of contact, and the experimental value. deep.

This Z is compared with X obtained by the above calculation, and the optimum gap is always set so that Z = X. When this value is obtained, the operation is continued as it is. On the other hand, when Z = X is not established, the electric motor (pulse motor) is operated according to the magnitude of the deviation,
The worm 8 and the worm wheel 11 are actuated to move the radial air bearing body 4 to the left and right, whereby the radial air bearing body 4 is contracted or expanded by the tapered surface of the radial air bearing body 4 and the main body 1. A gap between the body 4 and the shaft (rotating member) 2 is set to a predetermined value.

In the above embodiment, the rotational speed of the shaft, the temperature of the bearing and the temperature of the shaft were measured and the gap was controlled at a predetermined position. However, the bearing and the shaft are arranged very close to each other, If it is possible to approximate the temperature of one of the bearing and the shaft by measuring the temperature of the other, the temperature of the bearing can be detected as shown in FIG. 5, and the temperature of the shaft can be detected. By performing the detection based on the bearing temperature, it is possible to calculate the clearance by assuming the thermal expansion amount W of the shaft by using the temperature difference ΔT ₁ based on the bearing temperature T ₁ and the initial temperature.
By doing so, non-contact measurement of the shaft temperature can be omitted, and the device becomes inexpensive.

In the above embodiment, the radial air bearing body 4 is axially moved by the worm 8 and the worm wheel 11 to reduce the diameter of the radial air bearing body 4. At this time, however, the radial air bearing body 4 is reduced. 4 is also moving left and right along the axis. The amount of movement is up to about 5 mm in the axial direction, and the amount of change in diameter is about 0.2 mm. However, when it is not preferable that the support position of the bearing moves in the axial direction, the bearing position can be fixed as shown in FIG.

That is, in FIG. 6, an inner diameter 1d in the case body 1 is formed with a cylindrical hole instead of a conical shape, and a cylindrical member 14 having a conical hole 14a is attached to the cylindrical hole portion 1d. The radial air bearing body 4 having a conical outer peripheral surface is mounted in the cylindrical member 14. The cylindrical body 14 mounted between the radial air bearing body 4 and the case body 1 has a worm 8 and a worm wheel 1 like the radial air bearing body 4 in the embodiment of FIG. 1 described above.
1 is to move to the left and right in the axial direction. With this movement, the cylindrical body moves left and right, and the radial air bearing body 4 is reduced in diameter only without moving in the axial direction. Reference numeral 15 is a compression spring that holds the radial bearing body 4 in a fixed position.

In the above-described embodiment, the rotational speed of the shaft, the bearing temperature, and the shaft temperature, if necessary, are detected to calculate the clearance, and the clearance is set as the predetermined position. However, in the case where the device using the high-speed rotary bearing according to the present invention has a behavior of the bearing clearance due to centrifugal force expansion or thermal expansion that is reproducible with respect to the rotational speed of the shaft and the clearance is known in advance. It is also possible to detect only the rotation speed of the shaft without using the temperature sensor as described above and control the bearing clearance by using the rotation speed. That is, in this case, the rotation speed may be directly detected as in the above-described embodiment, or the rotation speed may be calculated by detecting the frequency of the current supplied to the stator member 7. In such a case, as shown in FIG. 8, the bearing drive pulse interlocked with the worm is selected in advance according to the curve shown in FIG. Based on the specified gap. When there is a difference in the bearing devices used, it is preferable to preset a unique control curve for each device.

[0046]

According to the present invention, the structure is supported by the air bearing having the variable bearing diameter mechanism capable of freely changing the clearance. At a low speed, the clearance is narrowed to increase the rigidity and relatively heavy cutting is enabled, and the high speed range is achieved. By widening the gap to prevent contact and seizure, it is possible to realize a spindle suitable for use from low speed to high speed.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a control circuit diagram of the embodiment shown in FIG.

FIG. 4 is a control flow chart of the embodiment shown in FIG.

FIG. 5 is a view corresponding to FIG. 4 of another embodiment.

FIG. 6 is an enlarged view of a main part of another embodiment.

FIG. 7 is a control circuit diagram of yet another embodiment.

FIG. 8 is a control diagram of the embodiment shown in FIG.

[Explanation of symbols]

 1 Case Main Body 2 Shaft 4 Radial Bearing Body 5 Rotor Member 6 Inner Cylinder 7 Stator Member 8 Worm 11 Worm Wheel

Claims (6)

[Claims] 1. A high-speed rotary air bearing device comprising a stationary member, a rotating member rotatable with respect to the stationary member, and a radial air bearing body provided between the stationary member and the rotating member, wherein the radial air bearing is provided. A control unit configured to move the body in a radial direction via a driving unit and change a clearance between the radial air bearing body and the rotating member according to a rotation speed of the rotating member. Variable air bearing device. 2. The control means includes a member for detecting the temperature of the radial air bearing body, and the drive means is operated so that the gap is at a predetermined position based on the detected temperature. The variable air bearing device described. 3. The control means includes a member for detecting the temperature of the rotating member, and the drive means is operated so that the gap is located at a predetermined position based on the detected temperature. Variable air bearing device. 4. The variable air bearing apparatus according to claim 1, wherein said control means detects the number of revolutions of said rotary member and program-controls said drive means according to said number of revolutions. 5. The variable type according to claim 1, wherein the radial air bearing body has a spring portion that expands and contracts in a circumferential direction and the outer peripheral portion has a tapered shape. Air bearing device. 6. The driving means comprises an electric motor, a worm connected to an output shaft of the electric motor, and a worm wheel meshing with the worm.
The variable air bearing device according to any one of items 1 to 5.